Electrolysis of copper



Patented Oct. 1, 1946 UNITED, STATES PATENT OFFICE ELECTROLYSI S OF COPPER William Clark Mason, Inspiration, Aria, assignor to Inspiration Consolidated Copper Company,

a corporationof Maine No Drawing. ApplicationMay 2'7, 1943, Serial No. 488,745 g This invention relates to electrolytic precipitation of metal, more particularly to the precipitation of copper from sulphuric acid electrolytes, and has for its object the provision of an improved method of controlling cathode sprouts. The wart-like .growths called sprouts, which form on cathodes as the metal is deposited, reduce the electrical efficiency and frequently become so large as to cause short circuits. The invention provides a simple and efiective method for inhibiting the growth of sprouts on copper cathodes with a resulting increase in the electrical eiiiciency.

In the electrolytic precipitation of copper as practiced heretofore, the sprouts form as needlelike or tree-like growths on the surface of the copper cathodes during the electrolytic deposition. These sprouts grow to such length that they may touch the anode, thus causing a short circuit.

I have discovered that an excess of concentrated sulphuric acid treated with a petroleum oil of naphthenic origin, such as California petroleum, has the property of inhibiting the growth of copper sprouts when the oil-treated acid is suitably incorporated in the electrolyte. In accordance with my invention, the concentrated sulphuric acid is treated with the petroleum, either crude or a distillation product, such as fuel oil, Diesel oil and the like, and a product of the reaction remains in the acid as the beneficial constituent which is added to the electrolyte along with the acid.

The oil-treated acid may be incorporated in the electrolyte in any suitable manner; for example, it may be added from time to time throughout the day to the electrolyte, to the plant supply of acid, or to the make-up acid which is used to replenish the acid losses.

In preparing the oil-treated acid, the California petroleum is agitated with strong sulphuric acid, for example, 78% to 95% acid, with the formation of water soluble and acid soluble products which remain in the acid, and an oily or sludgelike residue which separates on standing. In addition to the water and acid soluble products remaining in the acid, the acid contains materials in suspension, such as tars, which have not been completely identified. In using a fuel oil of about 16 gravity, about one part of oil is agitated with an excess of strong sulphuric acid, for example, one volume of oil to five volumes of acid, and the mixture is allowed to stand for several hours or until a heavy tar-like residue comes to the top and is discarded. Diesel oil may be used with an 1 Claim. (Cl. 204-108) excess of strong sulphuric acid, for'example, in amounts of about one volume of oil to from one to two and one-half volumes of acid. In using Diesel oil, however, acolorless oil comes to the top which may be recovered and used as a fuel.

In carrying out a method of the invention I may add continuously a small amount of oiltreated acid to the electrolyte as it enters the electrolytic plant. The quantity of this oiltreated acid should be about that of the acid necessary to treat the volume of oil required. The volume of oil required varieswith the appearance of the copper deposit, and to alarge extent varies with the amount of copper precipitated.

In operation involving the leachin of ore, it is more convenient to add the oil-treated acid to the larger volume of new acid required as this new acid has to be more or less uniformly added to the electrolyte. In such operations, it has been found that 1.4 gallons-to 2.8 gallons of oil have to be treated with an excess of acid for every ton of copper precipitated, the oil-treated acid containing the beneficial substance removed from the oil being incorporated in the electrolyte.

The quantity of oil to be treated with an excess of acid, necessary to yield an oil-treated acid to satisfy electrolyte requirements as to retarding sprout growth, may be expressed in the following manner: In an operation, for example, where about 2400 gallons of electrolyte flows to the electrolytic plant every minute, about 0.04 to 0.09

gallon ofoil are treated for every 1000 gallons flowing to the electrolytic plant.

The following illustrate specific examples:

Example I One volume of California fuel oil of about 16 gravity was agitated with five volumes of strong sulphuric acid for about one hour. After agitating, the mixture was allowed to stand for several hours. After standing, the heavy tar-like residue on top was skimmed off and discarded. The remaining liquid, which is the oil-treated acid. was then added to an electrolyte flowing to a set of electrolytic cells in the proportion of on gallon of oil-treated acid to about sixty gallons of plant acid. The growth of sprouts, and the electrode efficiencies of this set of cells were then compared to a duplicate set of cells using the same type of electrolyte but not having any of the above mixture added.

The average results of several such tests show the following results.

No oil- Oil-treated g z fg acid in electrolyte electrolyte Cathode efi ciency -.percent 71. 9

Anode efficiency. pe 73. 9

Difierence do. +1.3 Sprouts removed from cathode surfaces grams- 121 24 Difference "percent" -80 Ezmmple II One volume of California Diesel oil was agitated with 2 volumes of strong sulphuric acid Oil-treated acid in acld 1n electrolyte electrolyte Cathode efiicienc pcrcent 64. 8 66. 7 DitIerence. (1 +1. 9 Anode efficiency 63. l Difierence o. +1.5 Sprouts removed from cathode surfaces grams 191 19 Difierence "per cent" 90 It can be seen from the above examples that when small quantities of oil-treated acid containing organic reaction products produced in the treatment of California petroleum fractions by strong sulphuric acid are added to an electrolyte, the quantity of sprouts is greatly reduced. The improvements in the various electrode efficiences are due to the elimination of sprouts on the cathodes.

The cathode efficiency referred to herein means the amount of copper actually deposited, divided by the amount of copper that theoretically should have been deposited fOr th quantity of electric current that passed through the electrolyte. When this result is multiplied by 100, the answer is in percent.

The anode efiiciency referred to herein means the amount of ferrous iron oxidized to ferric iron at the surface of the anode, divided by the amount of ferrous ironthat theoretically should have been oxidized for the amount of copper precipitated out on the cathode. When this result is multiplied by 100, the answer is percent anode efficiency.

Iclaim:

In a, process for the production of electrolytic copper cathodes involving electrolytic precipitation of copper from a sulphuric-acid-containing electrolyte, the improvement which comprises inhibiting the formation of sprouts on the cathodes during electrolysis by adding to the electrolyte an oil-treated acid obtained by agitating one Volume of naphthenic crude oil with about five volumes of about 78% to 95% sulphuric acid, causing the oil-treated acid to settle and a tarlike material to form on top, and removing the tar-like material, the resulting oil-treated acid being added to the electrolyte in an amount corresponding to that produced by the treatment of about 1.4 to 2.8 gallons of the crude oil per ton of copper cathodes precipitated.

W. CLARK MASON. 

